Coins may become jammed in the bottom of the well. This can cause blockage.

Demonstration:A mounted coin track is placed on the edge of the well. The coins are then sent edge on to roll on the surface of the well. Gravity will force the coin to the center of the well and centrifugal force keeps the coin from falling directly into the well. As the orbit of the coin continues to decay towards the center the surface traveled in decreased and the speed of the coin increased. Finally the coin reaches the bottom or singularity of the well were it can not escape. This is designed to show how objects orbit around massive objects that bend space-time into a well-like structure. It also shows gravitational acceleration, orbital decay, and other classical physics concepts. .